Search the forum,

ducting

In telecommunications, an atmospheric duct is a horizontal layer in the lower atmosphere in which the vertical refractive index gradients are such that radio signals (and light rays) are guided or ducted, tend to follow the curvature of the Earth, and experience less attenuation in the ducts than they would if the ducts were not present. The duct acts as an atmospheric dielectric waveguide and limits the spread of the wavefront to only the horizontal dimension.Atmospheric ducting is a mode of propagation of electromagnetic radiation, usually in the lower layers of Earth’s atmosphere, where the waves are bent by atmospheric refraction. In over-the-horizon radar, ducting causes part of the radiated and target-reflection energy of a radar system to be guided over distances far greater than the normal radar range. It also causes long distance propagation of radio signals in bands that would normally be limited to line of sight.
Normally radio "ground waves" propagate along the surface as creeping waves. That is, they are only diffracted around the curvature of the earth. This is one reason that early long distance radio communication used long wavelengths. The best known exception is that HF (3–30 MHz.) waves are reflected by the ionosphere.
The reduced refractive index due to lower densities at the higher altitudes in the Earth's atmosphere bends the signals back toward the Earth. Signals in a higher refractive index layer, i.e., duct, tend to remain in that layer because of the reflection and refraction encountered at the boundary with a lower refractive index material. In some weather conditions, such as inversion layers, density changes so rapidly that waves are guided around the curvature of the earth at constant altitude.
Phenomena of atmospheric optics related to atmospheric ducting include the green flash, Fata Morgana, superior mirage, mock mirage of astronomical objects and the Novaya Zemlya effect.

View More On Wikipedia.org
  1. A

    Ducting for kitchen extractor fan

    We moved into a house with a gas Aga (I think converted from oil). The extraction pipe is fitted against and runs through an external wall, then up the outside of the external wall. The ducting pipe circumference is about 32cm, so about 10cm diameter. There is no extractor fan in the kitchen. We...
  2. T

    Kitchen extractor ducting to boiler to boiler flue.

    Morning, Im in a top floor tenement flat with access to the attic space. I have a combi boiler with flue that emits vertically up through the roof. My kitchen is situated internally with no easy access to an external wall. Could I fit a kitchen extractor that ducts vertically then right angles...
  3. G

    water supply sealing product

    Hi guys, organising a new water supply to my property, specs require a seal between the MDPE 25mm pipe and 50/63mm ducting, can't use builders foam and i can't find a product for this (severn trent shows what looks like a rubber reducing seal but i can't find it on any site
  4. M

    Ducting system for heating pipes in concrete

    Hi all. Does anyone have a manufactured system they use or make up their own out of plywood? Seen some ducts in BES but at £16 + vat for 3 metre is expensive and then you need to cut the ply top. Can kuterlex plastic coated copper pipe be buried in the screed without insulation or ducting...
  5. M

    Bosch Worcester Greenstar i System Boiler Ventillation requirements

    Hi all, Looking for advice on the ventillation of the Bosch Greenstar i System Boilers. I've had one fitted into a new home I've purchased and the developer missed a course of bricks out so the ceiling is too low to install a vent to the outside. The boiler is in a small room (2m x 1x1.8m x...
  6. M

    Ducting pipe for water supply pipe.

    Hi, I am renovating a house, and when I had a water meter fitted I took the opportunity to replace the lead supply pipe. It's only a short 2 meter run from the meter to the kitchen and I managed to source some 25mm MDPE pipe by asking a builder for any offcuts they had lying around at a...
  7. R

    pipe ducting in concrete

    Hi have got to price for fitting a couple of radiators in an extension, which will have a concrete base. I want to run the pipework in trunking, set in the base, can anyone suggest a supplier ? Have tried my usual merchants and they dont do it cheers
  8. R

    Replacing lead pipes and ducting

    Wonder if anyone can help? Replacing lead water pipe and have spoken to water board who are not very helpful and have told us to dig the trench etc and call once done for them to inspect. Cannot get any other advice from them!! What is classed as suitable ducting for the mdpe pipe to be put...
  9. O

    Extractor fan pumping down underfloor ?

    Can this be done ? Cant go any other way ! Its a under-staires toilet ? Can i go down under the floor with rigid ducting and to a air brick outside ? Its only a toilet and a sink in there !
  10. U

    Cooker hood ducting

    Want to place flat 220mm ducting along the top left hand corner of this picture (where it says 2.5 metres) to go to the outside wall, my question is how would i connect the ducting from the chimney bit from the cooker hood to the flat ducting so its flush along the length of the wall. The cooker...
  11. P

    Water marks near extractor fan on en-suite ceiling

    Hi I've been away for a few weeks but when i got back home i noticed these squiggly marks near the extractor fan in my upstairs en-suite...obviously they look like water marks. Could someone tell me what this is likely to indicate before i get the plumber in? (i'm hopeless at DIY!). The property...
  12. C

    Warm Air Heating Systems - Pros & Cons?

    Hi There, Can anyone offer advice or information regarding Warm Air Heating systems within the home? I am currently looking at homes to buy, and came across a home built in the 1970s with this system, but I know very little about them. Pros and Cons? any dangers etc? Any advice is greatly...
  13. W

    underfloor heating pipes

    i have a job in a bungalow where i need to move 2 radiators to other side of rooms. all the pipes are in pipe ducts with plywood covering pipes. i need to chase out the concrete floor to where the new rads will be situated, does anyone know of any trunking or ducting i can use.i have looked in...
  14. J

    gas pipe in under floor or above ceiling?

    Hi, i need some advice on where i should run the gas pipe inside a flat. it will be lpg gas coming underground into the property via a yellow plastic pipe and terminating in the boiler cupboard which is at the far end of the flat and the kitchen is at the other end of the flat. i need to...
Creating content since 2001. Untold Media.

OFFICIAL SPONSORS

OFFICIAL SPONSORS

Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock